The present invention relates to kitchen appliances and, more particularly, to motor-driven kitchen appliances.
A present trend in kitchen appliances includes designs especially adapted for suspending below kitchen cabinets, whereby such appliances are suspended clear of working surfaces below the cabinets. A product family of such suspended appliances is sold by the assignee of the present invention under the trademark Spacemaker.
Suspending an appliance below a cabinet denies access to the top of the appliance. Thus, in the case of a coffee maker or a popcorn popper, special means are required to permit administering coffee and water (in the case of a coffee maker) or unpopped kernels (in the case of a popcorn popper) through the front of the appliance.
The present invention is directed toward motor-driven knife sharpeners. A conventional knife sharpener rests upon a countertop and contains an electric motor driving a grinding wheel located near the top thereof. A pair of angled slots in the top of the knife sharpener guide a knife so that its edge contacts the side surfaces of the grinding wheel. Direct under-cabinet mounting denies access to the top slots in a conventional knife sharpener.
Although such a knife sharpener could be suspended far enough below the cabinet to permit access to top slots therein, styling considerations make this undesirable in some devices. The styling considerations arise because the knife sharpener of the present invention is only one member of a unified family of kitchen appliances. One characteristic of a successful unified family of appliances is a uniform facade, wherein each member of the family presents a unified facade blending with the remaining members of the family. In the present instance, it is determined that the other members of the family are suspended directly below the cabinets, without significant space above. Accordingly, mounting a knife sharpener with enough headroom to permit top access for inserting a knife blade would depart from the desired unified facade.
Some prior-art knife sharpeners are built in a combination which also includes a can opener. One side of the combination appliance includes the accessories for opening a can, and the other includes angled slots giving access to a grinding wheel. Both parts of the appliance are conventionally driven by a single electric motor. The motor speeds for the can-opening and knife-sharpening functions are preferably different. In most combination devices, the can opener is driven by a shaded pole motor running about 1500 RPM through reduction gearing, whereas the knife sharpener grinding wheel is connected directly to the motor shaft. An optimum speed for knife sharpener is about 5,000 feet per minute. A motor speed of 1500 RPM, suitable for driving the gearing of the can opener, drives the grinding wheel of the knife sharpener at a speed that is lower than the optimum. The economies gained from requiring only a single motor have encouraged manufacturers to accept the resulting compromise, even though the knife-sharpening function is not as effective as it could be.
A knife sharpener of the type having a rotating grinding wheel should be contacted by the knife edge with a uniform predetermined constant force. This objective is rarely attained. As the user inserts the knife blade through slot and into contact with the grinding wheel, the user may exert too much or too little force for satisfactory sharpening. If too little force is applied, the sharpening time is extended unnecessarily. If too much force is applied, the knife edge can be burned. Also, as the user moves the knife back and forth in the slot, and tilts the knife to accommodate curves in the cutting edge, a varying force can produce uneven metal removal.
Prior-art devices rely on a small amount of end play in the rotor of the driving motor combined with the tendency of such rotors to be centered by the magnetic field therein. Unfortunately, the available end play is too small, and the force constant is too variable to offer much of a solution to the problem of maintaining a constant grinding force.